Emergency stand-by electric service apparatus



April 29, 1969 F. G. PErKlNs T AL 7 3,441,829

EMERGENCY STANDBY ELECTRIC SERVICE APPARATUS Original Filed Dec. 16,1965 Sheet of 2 \f ::Z;g1

J0 ooooopnnn 1 .2w I llllllll INVENTOR Rafi/4K6 flaw r5 6M1 sad/4001mmr15 9& BY yw j ATTORNEY EMERGENCY STAND-BY ELECTRIC SERVICE APPARATUSOriginal Filed Dec. 16, 1965 Sheet 5 of 2 gii'g INVENTOR BY M ATTORNEYUnited States Patent US. Cl. 320-40 Claims ABSTRACT OF THE DISCLOSURE Abattery charging arrangement has a transformer-rectifier for producingdirect current connected by two conductors to a battery for charging it;in one of the conductors is an SRC and a control circuit for the SRCwhich includes a valve responsive to the voltage of the battery torender the SRC conductive when the battery voltage drops so as torecharge the battery, and a Zener diode in parallel with the controlvalve of the circuit to regulate the voltage at which the second valvebecomes operative; a light is so connected as to connect it to thebattery if the alternating current fails.

This application is a continuation of application No. 584,002 filed Oct.3, 1966 now abandoned and application No. 330,825 filed Dec. 16, 1963now abandoned.

This invention relates to emergency electrical systems, and moreparticularly to emergency lighting and alarm systems.

An object of the invention is to provide a novel and improved emergencylighting and alarm system which may be readily installed in buildingsand other structures as an adjunct to the normal lighting service toprovide emergency facilities upon failure of said service.

Another object of the invention is to provide an improved emergency orstand-by apparatus as above set forth, which is extremely reliable andfoolproof in its operation.

A further object of the invention is to provide an improved stand-bylighting and alarm apparatus in accordance with the above, which isrelatively simple in construction, inexpensive to fabricate andeconomical to maintain.

A still further object of the invention is to provide an improvedstand-by apparatus in accordance with the foregoing, which istrouble-free in operation and requires little or no servicing, orreplacement of parts throughout an extended period of use.

Still another object of the invention is to provide an improved stand-byemergency lighting system which will set off an alarm in the event offailure of the power source thereof, and which will also provide anindication of fuse failure in the stand-by circuits.

A feature of the invention resides in the provision of a novel auxiliarypower supply and control unit, which may be placed in a convenientlocation in the building, as determined by the available space.

A still further object of the present invention is to provide animproved auxiliary lighting or stand-by apparatus adapted to supply amultiplicity of stand-by circuits, wherein automatic energization of anyone or several of said circuits is provided for automatically inresponse to failure of one or several of the regular service circuits.

A further feature of the invention is to provide an emergency lightingand alarm system which has no moving parts whatsoever, in as much as alloperations are performed in conjunction with various solid statesemiconductor devices. This is accomplished in both the battery chargingand in the automatic connection of emergency electrical load.

A particular feature of the invention is the use of a Schmitt triggercircuit in conjunction with a Zener diode regulator to establish a fixedreference voltage at the emitter of the control transistor of thetrigger circuit so that in battery charging, a precise switching voltageto a different charging rate can be achieved, and with a resulting lowervoltage the hysteresis of the trigger circuit prevents the oscillatingswitching of the transistors of the trigger circuit.

Further objects and advantages of the invention will appear more fullyfrom the following description, particularly when take in conjunctionwith the accompanying drawings, which form a part thereof.

In the drawings:

FIG. 1 shows diagrammatically a circuit embodying the invention;

FIG. 2 shows part of a modified circuit; and

FIG. 3 shows a part of a further modification.

Referring to FIG. 1, the primary purpose of the invention as hereindisclosed is to provide for the lighting of emergency lights 2 in theevent of failure of the current in a conventional AC system 4 by meansof a battery 6, and to provide for recharging of this batteryautomatically whenever its charge drops below a predetermined value.

The circuit as shown has a pilot light 8 connected to the main circuit,as well as the primary winding of a transformer 10. A midpoint of thissecondary winding is connected to line 12, while the ends of thesecondary winding are connected by rectifiers D to line 14. Line 12 isconnected to the positive terminal of the battery while line 114 isconnected to the negative terminal through silicon-controlled rectifier16, and, in parallel with it, resistance R and rectifier D these beingjoined at a common point 11.

Resistances R and R are connected in series to line 12 and to thecollector of transistor Q The emitter of this transistor is connectedthrough switch S and resistance R; to point b. The base of transistor Qis connected to a midpoint of resistance R connected between lines 12and 14. Zener diode Z is connected in a line running from a pointbetween resistances R and R to line 14.

The resistance R, is connected at a point between resistance R and thecollector of transistor Q to the base of transistor Q The collector oftransistor Q is connected through a resistance R; to line 12, and itsemitter is connected through resistance R to resistance R The base oftransistor Q, is connected between resistance R and the collector oftransistor Q Its emitter is connected through resistance R to the line12, and its collector through the resistance R to the SRC gate 16.

The base of transistor Q, is connected to a point be tween resistance Rand the emitter of transistor Q and its emitter is connected to the line12. Its collector is connected through pilot light P to line 14.

The lamps 2 are connected at the side of the negative pole of battery band at the other side of the collectors of transistors Q and Q Theemitter of transistor Q is connected to the positive side of battery 6and its base is connected to the emitter of transistor Q The base oftransistor Q is connected to the collector of transistor Q The emitterof this transistor is connected to line 12 while its base is connectedto line 12 through resistance R and through resistance R of rectifier DD connected across the secondary of transformer 10.

During normal operation, as will be explained hereinafter, the battery 6is kept at full charge. During this operation, the main line current at4 is continuous, so that transformer 10 is energized. Through rectifierD D transistor Q is biased across resistance R and is conductive fromline 12 to line 14. Q and Q are not conducting because Q is effectivelyshorted by Q and R The lights are therefore not lighted. A condensor Cis provided to filter the Q bias.

If the power fails, transformer 10 is no longer energized and Q is nolonger conductive. Q and Q are then biased through their emitter-basesthrough R causing them to conduct and thus energize the emergency lights2. To obtain an on-off bias to Q a negative source is obtained directlyfrom the alternatign current source via independent rectification.

When normal power is restored, Q is again caused to conduct and thelights are cut off.

This lighting of the lights has caused a drain on battery 6. Assumingthat the battery has been discharged to a substantial extent, then thefollowing takes place when the power is restored and the emergencylights go off.

Current flows from voltage level a to b via: R R R Q base-emitter, R andR With transistor Q conducting, additional current paths are created. Asecond path forms through R, to Q where it joins with the first path.This causes Q to conduct and permits current to flow through: (a) Q,emitter-base to Q emitter-collector, R and SCR gate and (b) Qemitter-collector and pilot light P The path through R and Z establishesa definite voltage at junction b regardless of what the charging voltageis. This definite voltage is important as a reference for Q By means ofthese paths, the SCR is constantly being fired and thus conducting,which shorts out R and allows a higher current to flow through thebattery. Resistors R R and R are for biasing and thus control thevoltages and consequent currents to Q base, Q base, and SCR gate to thedesired values, respectively. Resistors R R R and R are primarily tolimit current. Also R and R being in series with R are part of the biascontrol of Q When the battery charging having progressed topredetermined point where the battery should now be transferred, asindicated by the charging voltage, to a low charge current rate, thevoltage across R has reached a value such that voltage at junction a isat the desired value as to cause Q to conduct. Upon Q conducting, a pathR R Q collector-emitter, and R is established. Since the resistancebetween junctions c and d via Q is negligible, compared to path throughR Q and R Q is effectively shorted out and ceases to conduct.

With Q non-conducting, Q loses its bias and turns oflf. This in turncauses: (a) Q; to shut off, extinguishing pilot light P and (b) removesthe SCR gate voltage and shuts off the SCR.

Current must now pass through R only, and thus is reduced to a muchlower value or trickle rate which may be adjusted to desired value byvarying the resistance R Immediately upon switching to lower tricklecharge rate, there is an immediate drop to a lower charging voltageacross the battery (and R Q continues to conduct while the remainder ofthe transistors and the SCR remain off or non-conducting. This abilityto resist changing back to the high charge condition (Q on and Q off) isdue to the inherent nature or characteristic of the circuit used, inconjunction with associated resistors, and is referred to as circuithysteresis. Although the voltage to Q base has been slightly reduced andis below its original required firing voltages, it still continues toconduct. It will continue to conduct unless the voltage drops to a valuebelow that required to turn on Q This drop below the turnoff voltagewill occur only when the battery has discharged below the predeterminedvalue because of charging failure and battery self discharge, ordischarging of the battery into the load or emergency lights.

A power failure will cause the emergency lights to be energized and thecharger shut off.

Cit

The immediate drain from the battery for the lights, removes the surfacevoltage from the battery and thus the voltage at junction a is less thanthe conducting voltage of Q which causes it to shut off. Q then resumesconducting. However, because there is no charging current present, thereis no current flow through Q and Q Accordingly the SCR and pilot light,P remain off.

The Zener diode, Z, has a fixed permanent voltage dropV Because of this,it frequently used as a voltage regulator. Thus when Q is conductingthere is a definite and fixed voltage at every point between and throughQ path. At point d, there is a voltage of This voltage is also the sameat e. Thus the emitter of Q, at point 3, is always at the definitevoltage of Now assume the pot R has been adjusted so that it will have anull or zero point at a certain battery voltage equal to +0.3 v., orassume E=3.0 volts, then the zero point would be 3.3 v. (The +0.3 v. isthe normal voltage increment required to turn on the transistor.)

Naturally as a battery is charged, it will start at less than this nullvoltage. As it becomes charged, the voltage at point 1 approaches thenull point. Then at the null point Q fires.

Without Zener Z to regulate and thus establish the fixed voltage of at dand e, these points too would increase somewhat as battery voltagerises. Thus it would be nearly impossible to obtain 0.3 v. increment forthe null point to occur. At least a definite switching voltage would notbe possible without a definite fixed voltage E at the emitter of Q OnceQ turns on, Q is shut off due to to much less resistance being in the Qcircuit and greatly reducing the current available for the base-emitteror Q the great majority of current passes collector-emitter of Q Whilethe battery charging voltage will be reduced below the originalturning-on voltage, the fact that Q stays on and Q remains off is due tothe hysteresis. Assuming that the battery was partially drained whilethe transistors were in this position (battery drain such as inadequatetrickle charge), when the battery had dropped to a certain voltage atthe end of the hysteresis limit, then Q would come on and shut off QFIG. 2 shows a modification using a transistor rather than an SCR. Otherthan the portion shown, it is identical with FIG. 1.

The base of transistor Q is connected to the collector of Q its emitterto line 12, and its collector to the bases of transistors Q and Q andthrough resistors R to the collectors of these transistors. Theresistance R is connected in parallel with transistors Q and Q,.

It the battery has been discharged and is to be recharged at a highrate, current flows from voltage levels a to b via: R R Q base-emitter,R and R With transistor Q conducting, additional current paths arecreated. A second path is formed through R to Q where it joins with thefirst path. This causes Q to conduct and permits current to flow throughQ; to and through pilot light P Q, is not conducting because Q hasplaced an effective short between Q base and emitter. Thus the basecurrent for Q from battery-through R is shunted through Qcollector-emitter.

The path through R and Z establishes a definite voltage at junction 11regardless of what the charging voltage is. This definite voltage isimportant as a reference for Q Q is biased via R from is collector andthus permitting Q; to conduct. With Q conducting, R is shorted out andallows a much higher charging current to flow through the battery.Resistors R R7 and R are primarily for biasing their respectivetransistors, while the remaining resistors are primarily to limitcurrent flow.

When battery charging having progressed to a predetermined point wherethe battery should now be transferred to the low charge current rate,the voltage across R has reached a value such voltage at junction a isat a desired value so as to cause Q to conduct. Upon Q conducting, apath R R Q collector-emitter, and R is established. Since the resistancebetween junction c and d via Q is negligible, compared to the paththrough R Q and R Q is effectively shorted out and ceases to conduct.

With Q non-conducting, Q loses its bias and turns 01f. This in turncauses: (a) Q; to shut off, extinguishing pilot light P Q is biased viaR and turns on to conduct current to and through R Under this situationthe base voltage of Q, is reversed. With Q losing its bias, it shuts offand would shut off Q6, except for bias via R Current is now reduced to amuch lower value for trickle rate which may be adjusted to any desiredvalue by varying the resistance of R The larger the resistance, thelower the changing rate upon switching to a lower charging rate, Q and Qcontinue to continue to conduct while the reamainder of transistorsremain off or nonconducting.

If a power failure causes the load to be energized and the charger shutoff, the lower battery voltage after use causes Q to revert to itsnon-conducting state while Q returns to conducting state when normalpower is restored and charging resumes.

Inasmuch as the SCR and transistors act purely as solid-state relays orremote switches, a relay of suitabie design could be used in place ofthese items. In models built using a relay, a current sensitive relaywas used- 0.35 watts, 400 ohms. Such a relay usually has low powercontacts and thus in some instances it would be used to trigger anotherrelay which would have heavier contacts required for higher currents. Asshown in the drawing, FIG. 3, the pilot light is connected at thejunction of the diode and contacts G instead of an additional transistorstage previously used, as Q; in the SCR circuit.

The switching On and Oil of the transistors is the same as in theprevious figures, the only difierence being that Q feeds the sensitiverelay coil G instead of the SCR gate with its voltage dropping resistor.Obviously the pilot light is on only when the relay contacts are closedsince there can be no reverse current flow through the diode.

To manually place the battery on high charge rate regardless of batteryvoltage, opening of S in the emitter circuit of Q prevents the Q circuitfrom effectively shorting out Q circuit, and thus Q remains conductingfor high charge regardless of battery voltage.

Temperature compensation of the battery voltage at which the circuitshould switch from high to low charge may be achieved by inserting athenmistor in the sensing circuit. By selecting the correct thermistor,compensation for an increase in temperature by switching at a lowerbattery voltage is achieved.

The use of a breaker as a current limiting device which willautomatically reset itself when the current overload has been removed ispreferably to normal fusing and manual reset breakers.

In circuits exceeding the approximately 70 volts necessary to ignite aneon light bulb, such a light bulb with suitable current limitingresistor may be used to shunt a current limiting device to indicate andsignal an alarm when the current limiting device is open andnon-conducting.

While we have described herein some embodiments of our invention, wewish it to be understood that we do not intend to limit ourselvesthereby except within the scope of the claims hereto or hereinafterappended.

What is claimed is:

1. In a battery charging arrangement having two conductors forconnection to the terminals of a battery and a direct current source,first valve means in one of said conductors, a control circuit for saidfirst valve means connected between said conductors and including meansresponsive to the reduction of the voltage of the battery below apredetermined amount to render said first valve means conductive, saidcontrol circuit further including a second valve means operative whenconducting to render said voltage-responsive means inoperative, wherebysaid first valve means in rendered non-conductive, said circuit having asubstantial impedance, and voltage-dependent valve means connectedacross said conductors in parallel with said second valve means toregulate the voltage at which said second valve means becomes operative.

2. In combination with an arrangement as claimed in claim 1, a source ofdirect current and a battery connected to said conductors, a load, andmeans, responsive to the failure of the direct current source, toconnect said load to said battery.

3. In an arrangement as claimed in claim 1, a relatively high resistanceconnected in parallel with said first valve means.

4. In a battery charging arrangement having two conductors forconnection to the terminals of a battery and a direct current source,first valve means in one of said conductors, a Schmitt trigger circuitconnected between said conductors and including means responsive to thereduction of the voltage of the battery below a predetermined amount torender said first valve means conductive, said circuit including asecond valve means operative when conducting to render saidvoltage-responsive means inoperative, whereby said first valve means isrendered non-conductive, and a voltage-dependent Zener diode connectedacross said conductors in parallel with said second valve :means toregulate the voltage at which said second valve means becomes operative.

5. In an arrangement as claimed in claim 4, a relatively high resistenceconnected in parallel with said first valve means.

References Cited UNITED STATES PATENTS 3,018,432 1/ 1962 Palmer.

3,123,759 3/1964 Grey 32040 3,160,805 12/1964 Lawson 320--39 3,281,63810/1966 Crawford 32040 3,281,639 10/1966 Potter et a1. 32039 X 3,310,7293/1967 Burgess et al. 323-22 X JOHN F. COUCH, Primary Examiner.

STANLEY WEINBERG, Assistant Examiner.

U.S. Cl. X.R. 32322, 38

